Like many others, while trying to install debian jessie on an rather old thinkpad, was stumped by the missing iwlwifi-5000-2/2/3/4/5 . Finally, I solved the problem as follows. I plugged an ethernet cable into the msachine, and proceded with the installations. When done, "I rebooted the machine, and then installed the file firmware-iwlwifi_0.43_all.deb, which can be rather easily found in the debian archives. I then shut the machine off, unplugged the ethernet cable, abnd revooted. I then clicked on the network icon on the panel, selected my usual wifi network, and I was in business.

Note that we can also load the missing firmwares in the installation process by putting firmware files, e.g. iwlwifi-5000-5.ucode, onto a USB stick and plug it in when prompted. And if you don't mind other non-free components, you can also install debian via unofficial CD images containing non-free firmwares.